Induction imaging with in-place development

ABSTRACT

A process for image reproduction comprises the steps of contacting a charge blocking surface on a photoreceptive body with a developer material containing charged toner particles, providing an electric field of predetermined polarity between the photoreceptor and a transfer medium for attracting the toner particles toward the photoreceptor surface, subjecting the photoreceptor to activating radiation in image configuration for inducing an electrostatic charge pattern in image configuration on the photoreceptor near an interface between the blocking layer and the developer material and providing an electric field of opposite polarity between the photoreceptor and the transfer medium for transferring the toner particles in image configuration to the transfer medium. Automated copying apparatus and photographic apparatus in accordance with features of the invention are provided.

United States Patent Schmidlin [451 Apr. 15, 1975 [75] Inventor: Fred W.Schmidlin, Pittsford, N.Y.

[73] Assignee: Xerox Corporation, Rochester, N.Y.

[22] Filed: Aug. 29, 1973 [21] Appl. No.: 392,600

Related U.S. Application Data [62] Division of Ser. No. 212,220, Dec.27, 1971,

abandoned.

[52] U.S. Cl. 96/1.4; 96/l.3; 204/181 [51] Int. Cl G03g 13/14 [58] Fieldof Search 96/1 PE, 1.3, 1.4; 204/181 PE [56] References Cited UNITEDSTATES PATENTS 3,511,651 5/1970 Rosenberg 96/1 PE 3,607,256 9/1971Si1verberg.... 91/1 PE 3,674,475 7/1972 Silverberg 96/1 PE PrimaryExaminer-Norman G. Torchin Assistant E.taminer-Judson R. Hightower [57]ABSTRACT A process for image reproduction comprises the steps ofcontacting a charge blocking surface on a photoreceptive body with adeveloper material containing charged toner particles, providing anelectric field of predetermined polarity between the photoreceptor and atransfer medium for attracting the toner particles toward thephotoreceptor surface, subjecting the photoreceptor to activatingradiation in image configuration for inducing an electrostatic chargepattern in image configuration on the photoreceptor near an interfacebetween the blocking layer and the developer material and providing anelectric field of opposite polarity between the photoreceptor and thetransfer medium for transferring the toner particles in imageconfiguration to the transfer medium. Automated copying apparatus andphotographic apparatus in accordance with features of the invention areprovided.

10 Claims, 15 Drawing Figures INDUCTION IMAGING WITH IN-PLACEDEVELOPMENT This is a division of application Ser. No. 212,220 filedDec. 27, I971, now abandoned.

This invention relates to electrostatography. The invention relates moreparticularly to an improved process and apparatus forelectrostatography.

In electrostatography an image is reproduced by initially creating anelectric charge pattern in image configuration and subsequentlyutilizing this charge pattern to provide a copy of the image. In onesystem, the image charge pattern comprises a latent electrostatic chargewhich is formed on a surface of a photoresponsive body. The latent imageis then developed by contacting the surface with a developer materialand the developed image is subsequently transferred to a record medium.In another known system, an electric charge pattern is established onpigmented particles which particles are then deposited on a recordmedium.

In the imaging system wherein a latent electrostatic image is formed onthe surface of a photoresponsive body and a developer material contactsthe image retention surface, a restriction on processing speed arises asa result of the limited rate at which the developer material can betransported from a source to the surface. This is particularly true withthe well-known cascade development. Another significant limitation isthe relatively weak interaction between the electrostatic latent imageand the developer material. This interaction depends upon severalfactors which in general dictate the use of a relatively thick andcorrespondingly non-flexible photoreceptor body for the image retentionsurface. Additionallly, separate charging, exposing and developing stepsare performed in this imaging process and the performance of these stepsis timeconsuming and requires relatively expensive and complexapparatus.

Various modifications have been proposed in order to overcome several ofthese limitations. In U.S. Pat. No. 2,892,709 to E. F. Mayer, thesurface of a photoconductor is charged in image configuration through aliquid developer layer while the photoconductor is exposed to a lightimage. The photoconductor accepts charge in the relatively darker areasthereby forming an electrostatic image on the photoconductor. Tonerparticles in the liquid developer are drawn to, or precipitate on thesurface of the photoconductor in the charged areas thereby forming avisible image. This process is ineffective since it requires theattraction of a charge of one polarity for charging the photoconductorand subsequently requires the attraction of a pigment of an oppositepolarity. In another arrangement which is disclosed and claimed incopending U.S. Patent Application Ser. No. 104,389 filed on Jan. 6,1971, and which is assigned to the assignee of this invention, anelectrophoretic imaging process is provided wherein a suspension oftoner particles in an insulating liquid is positioned between aphotoconductive electrode and a second electrode. An electric field isestablished between the electrodes while the photoconductor is exposedto imagewise radiation thereby resulting in an exchange of chargebetween the photoconductive electrode and toner particles and causingreplusion of the toner particles from the surface of the photoconductiveelectrode in image configuration. In a further arrangement described inU.S. Pat. No. 2,968,552, to Gundlach which is assigned to the assigneeof this invention. particles are deposited on a photoconductive surfaceand a uniform electrostatic charge is then formed thereon. A transfermemdium contacts the charged particles while the particles are exposedthrough the photoconductive surface in order to provide simultaneousexposure and development.

It is an object of this invention to provide an improved imaging processand apparatus.

Another object of the invention is to provide an improved imaging andin-place development process.

Another object of the invention is to provide an improved imagingprocess and apparatus which avoids one or more of the above enumerateddisadvantages accompanying prior art devices.

Another object of the invention is to provide an electrostaticreproduction process adapted for utilizing a relatively thinphotoconductive body.

Another object of the invention is to provide an electrostaticreproduction process of enhanced sensitivity.

Still another object of the invention is to provide an improvedelectrostatic process adapted for photographic use.

In accordance with the features of this invention, a process for imagereproduction comprises the steps of contacting a charge blocking surfaceon a photoreceptive body with a developer material containing chargedtoner particles, providing an electric field of predetermined polaritybetween the photoreceptor and the transfer medium for uniformlyattracting the toner particles toward the photoreceptor surface,subjecting the photoreceptor to activating radiation in imageconfiguration for inducing an electrostatic charge pattern in imageconfiguration on the photoreceptor near an interface between theblocking layer and the developer material and providing an electricfield of opposite polarity between the photoreceptor and the transfermedium for transferring the toner particles in image configuration tothe transfer medium. Automated apparatus and photographic apparatus inaccordance with features of the invention are provided.

These and other objects and features of the invention will becomeapparent with reference to the following specification and to thedrawings wherein:

FIG. 1 is a side view in section of an imaging assembly constructed inaccordance with features of this invention;

FIG. 2A 2C are diagramatic representation of process steps in accordancewith one embodiment of this invention;

FIGS. 3A and 3B are diagramatic representations of process steps inaccordance with another embodiment of the invention;

FIGS. 4A and 4B are diagrammatic representation of process steps inaccordance with another embodiment of the invention;

FIG. 5 is a plan view of a camera constructed in accordance withfeatures of this invention;

FIG. 6 is a side view of an alternative imaging assembly modified inaccordance with features of this invention for use with the camera ofFIG. 3;

FIG. 7 is a schematic view of an automated apparatus for practicing thepresent invention;

FIG. 8 is an enlarged view of a section of a transfer and developer beltutilized with the apparatus of FIG.

FIG. 9 is a sectional view of an imaging belt taken along lines 99 ofFIG.

FIG. 10 is a schematic view of an alternative means for cleaning theimaging belt of the apparatus of FIG. 5 and for recording acomplementary image; and,

FIG. 11 is a schematic diagram of an alternative arrangement exposingthe photoreceptor 5 and for enhancing its sensitivity.

Referring now to FIG. 1, an imaging assembly comprises a film ofdeveloping material 10 backed by an image transfer and record medium 12.The transfer and record medium 12 comprises a white paper material forexample while the developer film 10 is uniformly coated on the paper 12to a thickness determined by the maximum optical density desired. Whilethe transfer and record mediums are provided by the single body 12, thetransfer and record mediums may comprise separate bodies as is describedhereinafter with respect to FIG. 5. The developer material comprises,for example, a colloidal suspension of a toner material such as charcoalin a liquid of suitable viscosity and having a chemical potentialrelative to the toner for providing that the toner acquires a charge perparticle within a specified range. Various suitable suspensions areknown for use in the electrostatographic arts. The developer material 10faces a body of photoreceptor material 14 which is positioned on atransparent backing 16. The photoreceptor body is formed fromaphotoresponsive material, as for example, cadmium sulfur seleniumparticles in a suitable binder. An electric charge transfer blockinglayer 18 is established at an interface between the photoreceptor body14 and the developer material 10. The blocking layer 18 may be integralwith the body 14 and formed by natural or artificially prepared surfaceelectric charge traps or it may be provided by a thin film of electricalinsulating material such as Mylar having a thickness of less than 1micron. In use, the imaging assembly is positioned between an electrode20 and a transparent electrode 22 as illustrated in FIG. 2. Theelectrode 22 is fabricated of a body of glass, for example having a thinfilm of transparent, electrically conductive material deposited thereon.The conductive transparent film may comprise tin oxide for example.Alternatively, electrode 22 comprises an integral part of the substrate16 in the form of a transparent conductive layer.

The process steps in accordance with features of this invention areillustrated in FIG. 2A, 2B and 2C. The imaging assembly of FIG. 1 ispositioned between electrodes 20 and 22 as shown in FIG. 2A. A source 24of adjustable DC. potential is coupled between the electrodes 20 and 22by suitable wiring and a switch 26. The source of potential and theelectrodes provide for the establishment of an electric field gradientacross the imaging assembly. A potential is applied to these electrodesby operating the switch 26 as shown in FIG. 2B. Simultaneously, theimaging assembly is exposed to an image on a transparency 28 by a lamp30 and a lens 32 which focuses the image at the photoreceptor surface.

As indicated hereinbefore, developer material includes toner particlessuspended in an insulating liquid. These particles acquire a charge as aresult of their chemical potential relative to the insulating liquid inwhich they are suspended. In the exemplary arrangement of FIG. 28, theseparticles are shown to have acquired a relatively positive charge. Theapplication of an electric potential between electrodes 20 and 22 havinga polarity as indicated in FIG. 2B establishes a force on thesepositively charged toner particles which causes them to travel throughthe insulating liquid to the barrier surface 18. The positively chargedtoner particles are thus uniformly distributed along this barriersurface. Exposure of the photoreceptive material 14 to the image inducesan electrostatic image at the surface of the photoreceptor. This imageis a negative of the original subject considered to be dark with respectto the background and is represented in FIG. 28 by the accumulation ofnegative charges near the surface of the photoreceptor. Thiselectrostatic image remains temporarily fixed thereto due to thetrapping of the charge by the blocking layer 18. The establishment ofthis negative charge increases the magnitude of electrostatic forceexerted on the positively charged toner particles in those areasconforming to a negative of the image. The polarity of the voltageapplied between the electrodes 20 and 22 is then reversed as indicatedin FIG. 2C. This reversal in polarity alters the direction of theelectric field acting on the toner particles in those areas of the platecorresponding to very little or no light exposure and causes theseparticles to be drawn toward the record medium 12. By increasing thepotential which is applied by the source 24 between the electrodes 20and 22 as shown in FIG. 2C, the restraining force on the toner particleswill be overcome in the unexposed or weakly exposed areas and the tonerparticles in such areas will be attracted toward the transfer and recordmedium 20. Thus, a positive of the image to be reproduced is establishedinitially on a record me dium while a negative of the same image isestablished at the surface of the photoreceptor. This process isparticularly advantageous in that it provides for direct inplanedevelopment accompanying an induced charge in image configuration.

FIGS. 3A and 3B illustrate an alternative embodiment of the imagingprocess of the invention for forming a positive image on the recordmedium 12 and a complementary image at the photoreceptor. The polar ityof the pigment particles and the polarity of the photoconductor chargesare opposite to the polarities employed with respect to the process ofFIG. 2. Similarly, the polarity of the applied potentials is alsoreversed. Suitable photoconductive materials capable of transportingpositive charges are arsenic triselenide or other arsenic seleniumalloys and polyvinyl carbazole. Negative pigment particles in carriersare well-known and include photosensitive particles and mixtures as aredisclosed in US. Pat. No. 3,384,566.

In addition to forming a negative image on the photoreceptor and apositive image on a record medium with the process thus described, apositive image can be formed on the photoreceptor and a negative imageon the record medium. This complementary imaging process is accomplishedby initially precharging the surface of the photoreceptor to a uniformrelatively large potential having a polarity differing from the polarityof the charge on the pigmented particles. The pigmented particles travelto the interface surface as a result of the electrostatic force exertedon the particles both by this potential and the potential provided bythe battery 24 which is coupled between electrodes 20 and 22 forincreasing the effective electric field forces operating on the pigmentparticles. FIG. 4A illustrates the alignment of the pigment particlesand the precharge on the surface of the photoconductive body. Thephotoconductor is then subjected to activating radiation in imageconfiguration by the light source 30, the transparency 28 and thefocusing lens 32 while the polarity of the potential applied between theelectrodes is reversed. Positive photoconductor charges travel throughthe photoconductor to the blocking surface 18 in exposed areas. Themagnitude of the potential derived from the source 24 and appliedbetween electrodes as illustrated in FIG. 4B is selected to be slightlyless than that produced by the uniform charge which was initially formedon the surface of the photoconductor 14. This results in a field actingon the pigment particles which forces them to be attracted toward thephotoconductor. Supplementation of the above field by the field producedby the positive photoconductor charges results in reversal of the netfield acting on the charged pigment particles in the exposed areas whichare thus drawn to the record medium as is illustrated in FIG. 4B. Apositive of the image being reproduced remains on the interface surface18 while a negative of the image being produced is established on therecord medium 12.

Negative imaging as illustrated in FIG. 4 utilizes the establishment ofa relatively high electric field which is provided by the establishmentof a precharge on the surface of the photoconductor 14. With the use ofan ambipolar photoconductor such as selenium, the surface precharge canbe established by initially exposing the photoconductor to uniformactivating electromagnetic radiation while simultaneously applying apotential between the electrodes which differs in polarity with respectto the potential which is applied thereto during the imaging andtransfer step. As illustrated in FIG. 4A, the ambipolar photoconductorwill transport negative charge to the interface surface during thischarging step. Subsequently, when the polarity of the applied potentialis reversed, the photoconductor will transfer positive charge to theinterface surface in image configuration. Alternatively, when thephotoconductor comprises a material which is not ambipolar such asarsenic directly to the surface of the photoreceptor prior to assemblyof the sandwich configuration by means such as corona charging or othersuitable charging techniques.

A camera adapted for employing the process of this invention isillustrated in FIG. 5. The camera includes a boxshaped enclosure 40having upright guides 42 and 44 positioned therein. These guides aresecured to side walls of the enclosure and support electrodes 46 and 48therebetween. The electrodes are spaced apart a distance for receiving afilm strip in position therebetween. A potential is coupled to each ofthe electrodes from a voltage source which is not shown in detail butwhich is positioned whithin a battery operated power pack which ismounted to the enclosure 40 and is represented by the rectangularsegment 50. The power pack may comprise any of the conventionalhighvoltage sources and the potential provided by this source is coupledvia feed through connectors 52 and 54 as well as lead-in wires to theelectrodes 46 and 48 respectively. A switch 58 is provided for applyingpotentials to the electrodes during the imaging step. A switch 60 isalso provided for reversing the polarity of the potential applied to theelectrodes during the developing step. A bellows 62 and lens 64 areprovided for the camera along with the usual shutter and aperturearrangements which are well known and which for purposes of clarity inthe drawings are not illustrated in FIG. 3.

FIG. 6 illustrates an alternative form of the imaging assembly which isparticularly useful with the camera of FIG. 5. Those elements of FIG. 1which are illustrated in FIG. 4 and perform the same functions bear thesame reference numerals. Although the imaging arrangement illustrated inFIG. I operates satisfactorily for photographic applications, film ofhigher speed, resolution and image quality can be achieved through theuse of conductive coatings on both the developer backing and thephotoreceptor substrate. A conductive film 66 and an insulating film 68are positioned between the record medium 12 and the developer material10. The conductor film 66 has a thickness on the order of I mil or lesswhile the insulating film 70 and a conductive film 72 are positionedbetween the photoreceptor l4 and transparent electrode 16. The use ofthe conductive films 66 and 72 provides greater coupling between theelectrostatic image at the photoreceptor and the developer. Further, theuse of these films increases the sensivity of the photoreceptor andprovides for the use of relatively lower voltages in carrying out boththe imaging and developing steps then are required with the imagingassembly described with respect to FIGS. 1 and 2.

An automated apparatus for continuously imaging and developing inaccordance with the process of this invention is illustrated in FIG. 7.The apparatus includes an endless support belt which is positioned aboutdrum rollers 82 and 84 and is transported in counterclockwise directionby these rollers. The belt 80 is formed of Mylar or other transparentsupport material and includes a film 88 (FIG. 9) of transparentconductive material deposited on a surface of the belt 80 and a film 86of photoreceptor material deposited on the transparent substrate 88. Theconductive film 88 comprises a material which produces an electriccharge blocking contact with the photoreceptor. Alternatively, a thininsulating layer between the conductor and photoreceptor is provided.The photoreceptor material comprises for example cadmium sulfur seleniumin a suitable binder while the transparent conductive film 88 comprisesfor example tin oxide. A wiper contact 90 is positioned in contact withthe conductive film and is coupled to ground potential for maintainingthe film and the belt at ground potential.

A transfer and developer belt 92 is provided for transporting developermaterial to imaging and developing stations and for transporting adeveloped image to a transfer station. The belt 92 is formed of anelectrically insulating material and includes a plurality ofelectrically conductive metal strips 94 which are embedded in the belt92 and extend across the width of the belt. Each segment is spacedlongitudinally from an adjacent one and a portion of each conductivesegment is exposed at the surface of the belt for contact with animaging wiper brush 96 and a developing wiper brush 98. The belt 94 ispositioned about'drum rollers 100 and 102 which rotate and transport thebelt in a clockwise direction in contact with the photoreceptor surface86. Developer material 104 is contained in a reservoir and is depositedon the outer surface of the belt 92 by a conveyor mechanism 106including a number of buckets positioned on an endless chain whichextend in a sump area and convey the material to a location at which itis cascaded over the surface of the belt 92. A

negative potential is provided by a voltage source 108 and is applied tothe drums 100 and 102 and to the segments 94 through the wiper brush 98in the vicinity of the developing and coating station for establishingan electrostatic binding force on the belt which causes the developermaterial to adhere to the outer surface of the belt. A record mediumcomprising a web or continuous strip of paper 110 is provided and ismaintained in contact with the outer surface of the belt 92. The stripis derived from a reel I12 and is fed past a grounded roller 113 to atake-up reel 114. The roller is spaced opposite an electrode 115 towhich a positive potential is applied from a source 116 for causingelectrostatic transfer of the image to the web. During operation, thepowdered surface of the developing belt 92 is cleaned by a groundedrotating brush 117 prior to recoating while the photoreceptivc surface86 on the belt 80 is cleaned by rotating brush 118.

In operation, the belts 80 and 94 are transported in contact through animaging station and then through a developing station. At the imagingstation, the contact brush 96 which is coupled to a source of electricalpotential 120 simultaneously contacts a plurality of segments 94 andthese segments are thereby maintained at a positive potential. A subjectwhich is to be reproduced from a transparency 122 for example, ispositioned at the imaging station and exosure of the photoreceptive filmto this transparency is provided by a light source 124, a shutter 126and a lens 128. The shutter 126 is operated at a rate which provides foran exposure of the moving photoreceptor. Alternatively, the transparencymay be transported at the same velocity as the photoreceptor. In thesame manner as was described with respect to FIG. 2, the chargedparticles progress to the surface of the photoreceptor by virtue of thepotential applied thereto and an electric charge in image configurationis established on the photoreceptor surface. The surface of thephotoreceptor is adapted to provide sufficient charge traps forretaining the charge in image configuration. The moving belts progressto the development station at which a potential of opposite polarityderived from the source 108 is applied between the belt 92 and thephotoreceptor. The toner particles travel toward and adhere to the outersurface of the belt 92 in image configuration. This developed image istransported by the belt 92 to a transfer station at which location theouter surface of the belt 92 contacts the transfer record medium 110 andis electrostatically tramsferred thereto. The image which is transferredto the medium 110 may be fixed thereto by heat fusing or by other knownmeans.

Subsequent to the transfer, the developer belt 92 is cleaned and retonedat the toning station. The toner is applied to the belt 92electrostatically in order to control the amount and hence the maximumoptical density in the developed image. While the use ofa dry form ofdeveloping material has been described with respect to FIG. 7, greatercontrol and sensitivity can be accomplished by electrophoreticextraction of toner particles from a liquid bath or mix. A thin layer ofinsulating fluid then remains on the toner and reduces thenonelectrostatic component of adhesion and thereby increases thesensitivity of the system. A reduced nonelectrstatic adhesion reducesthe electrostatic force required for discminating to which electrode thetoner clings to.

The belt is cleaned after exposure, as was indicated, by the brush 118.An alternative arrangement for cleaning the belt 80 and forsimultaneously providing a record of a complementary image is providedby the arrangement illustrated in FIG. 10. Those elements of FIG. 10which perform the same functions as elements of FIG. 7 bear the samereference numerals. In FIG. 10, a receiving sheet 132 is provided and issupplied from a roll 134 and is taken up by a roll 138. The sheet 132 isbacked at a location intermediate the feed and take-up rolls by anegatively biases roller 136 which is spaced opposite an erase lamp 130.The combination of the erase lamp and the negative biased roller 136induces a uniform positive charge on the photoreceptor and therebyproduces an electrostatic force which causes transfer of pigment fromthe photoreceptor to receiver sheet 132. This transferred pigment formsa negative of the original image. A grounded electrode 142 is placedopposite the erase lamp and behind the transfer-cleaning station inorder to return the surface of the photoreceptor to zero potential.Alternatively, the electrode 142 can be biased to some preferrednegative voltage to assist the development process.

The described process and apparatus are particularly advantageous sincethey provide for the use of relatively thin and hence more flexiblephotoconductors. The thickness of the latter need only be comparable tothe diameter of the toner particles which is typically a few microns.Thus, the photoconductor in accordance with this invention need only bea few microns thick. Photoreceptors capable of secondary conduction ortrue quantum gain are advantageously used since a counter electrode ispresent during exposure. This includes utilization of avalanche gainwhich occurs in two phase or binder type photoreceptors. Highersensitivity photoreceptors are also feasible for use in the dc scribedprocess and apparatus since they need only be sensitized duringexposure. Image degradation due to breakdown or corona which has beenencountered in prior apparatus is avoided since development isaccomplished in place before the electrostatic image is subjected torelatively large air gaps. High process speeds are now possiblle sincethe relatively slower prior art steps of toning, transfer and fusing canbe effectively done in parallel through the use of more extended zones.Additionally, as the toner is extracted from a liquid, the liquid canact as a lubricant for facilitating cleaning and effecting greater wearresistance of the belts.

In a particular example not to be deemed liminting in any manner, animaging assembly comprising a film of developing material consisting ofN1 Lawter Magenta B 2l54/Eicosane is deposited on a recording mediumcomprising Sterling Litho paper. The photoconductor comprises a 15 to 20micron layer of 1/1 Monastral Red B/P PE-20O resin deposited on a 2 milthickness of Mylar. The Mylar is positioned on a NESA body whichconsists of tin oxide deposited on glass. A blocking layer is formed ofa film of styrene-n-butylmethacrylate having a thickness of less than 1micron. The assembly is exposed with a potential of 7 kilovolts whereinthe Mylar is negatively polarized with respect to the Litho paper duringan imaging step and the image is then developed by applying a reversepotential of 500 volts and increasing this potential to 1500 volts whilethe Mylar is maintained positive with respect to the Litho paper. Asatisfactory positive image is thereby produced.

While I have illustrated and described particular embodiments of myinvention, it will be understood that various modifications may be madetherein without departing from the spirit of the invention and the scopeof the appended claims. What is claimed is: l. A method of imagereproduction comprising the steps of:

depositing a developer material comprising electrically charged tonerparticles dispersed in an insulating liquid between an electric chargetransfer blocking means, which is positioned adjacent a surface of aphotoconductor body, and an image transfer medium; establishing anelectric field of predetermined polarity between said photoconductor andsaid transfer medium for exerting an electrostatic force on said chargedparticles and causing said particles to uniformly migrate toward saidphotoconductor, subjecting said photoconductor to activatingelectromagnetic radiation in image configuration to increase theelectrostatic force exerted on said particles adjacent light struckareas of said photoconductor, and establishing between saidphotoconductor and transfer medium an electric field of oppositepolarity and having a magnitude for causing the transfer of particlescorresponding to non-light struck areas of said photoconductor totransfer in image configuration to said transfer medium to form an imagethereon, said magnitude being insufficient to re move particlescorresponding to light struck areas of said photoconductor therebyproviding an image on said charge blocking means formed by said transferof particles in non-light struck areas.

2. The method of claim 1 wherein said toner particles and insulatingliquid are selected for trioboelectrically establishing a resultantelectrical charge of predetermined polarity on said toner particles.

3. The method of claim 1 wherein said transfer medium comprises a recordmedium.

4. The method of claim 1 wherein said electric charge blocking meanscomprises charge traps integrally formed in a surface of saidphotoconductor body.

5. The method of claim 1 wherein said electric charge blocking meanscomprises a thin film of electrically insulating material positionedadjacent a surface of said photoconductor.

6. The method of claim 1 wherein said electric fields are provided bycoupling a source of potential between said photoconductor and saidrecord medium.

7. The method of claim 1 wherein said electric field of predeterminedpolarity is provided by establishing a uniform electric charge at asurface of the photoconductor.

8. The method of claim 1 wherein said charge is established on saidphotoconductor surface of corona charging.

9. The method of claim 1 wherein said charge is established on saidphotoconductor surface by subjecting said photoconductor to uniformactivating electromagnetic radiation and simultaneously establishing anelectric field between said photoconductor and said record medium.

10. The method of claim 1 wherein said photoconductor surface comprisesa thin film formed on a transport body which travels in contact with asecond transport body, and said developing material is applied to saidsecond transport body.

1. A METHOD OF IMAGE REPRODUCTION COMPRISING THE STEPS OF: DEPOSITING ADEVELOPER MATERIAL COMPRISING ELECTRICALLY CHARGED TONER PARTICLESDISPERSED IN AN INSULATING LIQUID BETWEEN AN ELECTRIC CHARGE TRANSFERBLOCKING MEANS, WHICH IS POSITIONED ADJACENT A SURFACE OF APHOTOCONDUCTOR BODY, AND AND IMAGE TRANSFER MEDIUM; ESTABLISHING ANELECTRIC FIELD OF PERDETERMINED POLARITY BETWEEN SAID PHOTOCONDUCTOR ANDSAID TRANSFER MEDIUM FOR EXERTING AN ELECTROSATIC FORCE ON SAID CHARGEDPARTICLES AND CAUSING SAID PRATICLES TO UNIFORMLY MIGRATE TOWARD SAIDPHOTOCONDUCTOR, SUBJECTING SAID PHOTOCONDUCTOR TO ACTIVATINGELECTROMAGNETIC RADIATION IN IMAGE CONFIGURATION TO INCREASE THEELECTROSTATIC FORCE EXERTED ON SAID PARTICLES ADJACENT LIGHT STRUCTAREAS OF SAID PHOTOCONDUCTOR, AND ESTABLISHING BETWEEN SAIDPHOTOCONDUCTOR AND TRANSFER MEDIUM AN ELECTRIC FIELD OF OPPOSITEPOLARITY AND HAVING A MAGNITUDE FOR CAUSING THE TRANSFER OF PARTICLESCORRESPONDING TO NON-LIGHT STRUCK AREAS OF SAID PHOTOCONDUCTOR TOTRANSFER IN IMAGE CONFIGURATION TO SAID TRANSFER MEDIUM TO FORM AN IMAGETHEREON, SAID MAGNITUDE BEING INSUFFICIENT TO REMOVE PARTICLESCORRESPONDING TO LIGHT STRUCK AREAS OF SAID PHOTOCONDUCTOR THEREBYPROVIDING AN IMAGE ON SAID CHARGE BLOCKING MEANS FORMED BY SAID TRANSFEROF PARTICLES IN NON-LIGHT STRUCK AREAS.
 2. The method of claim 1 whereinsaid toner particles and insulating liquid are selected fortrioboelectrically establishing a resultant electrical charge ofpredetermined polarity on said toner particles.
 3. The method of claim 1wherein said transfer medium comprises a record medium.
 4. The method ofclaim 1 wherein said electric charge blocking means comprises chargetraps integrally formed in a surface of said photoconductor body.
 5. Themethod of claim 1 wherein said electric charge blocking means comprisesa thin film of electrically insulating material positioned adjacent asurface of said photoconductor.
 6. The method of claim 1 wherein saidelectric fields are provided by coupling a source of potential betweensaid photoconductor and said record medium.
 7. The method of claim 1wherein said electric field of predetermined polarity is provided byestablishing a uniform electric charge at a surface of thephotoconductor.
 8. The method of claim 1 wherein said charge isestablished on said photoconductor surface of corona charging.
 9. Themethod of claim 1 wherein said charge is established on saidphotoconductor surface by subjecting said photoconductor to uniformactivating electromagnetic radiation and simultaneously establishing anelectric field between said photoconductor and said record medium. 10.The method of claim 1 wherein said photoconductor surface comprises athin film formed on a transport body which travels in contact with asecond transport body, and said developing material is applied to saidsecond transport body.